In the Long Term Evolution (LTE) system, Sounding Reference Signal (SRS) may be used to perform LTE uplink scheduling, synchronization and power control, so SRS plays an important role in the LTE system. The minimum bandwidth for SRS resource allocation is four RBs (Resource Blocks), each of which is composed of 12 subcarriers on the frequency domain, and the total number of RBs of SRS bandwidth resources is determined collectively by system bandwidth, the bandwidth occupied by a PUCCH (Physical Uplink Control Channel) and the bandwidth occupied by a PRACH (Physical Random Access Channel). It is regulated in the LTE protocol that the SRS signal can only be transmitted in the last symbol of the uplink conventional subframe, and as for TDD (Time Division Duplexing), if the UpPTS (Uplink Pilot Time Slot) have two symbols, then the SRS signal can be transmitted in two symbols therein at most. The SRS resources have a Tree structure in the frequency domain so as to indicate the resources that can be allocated. Such a tree structure is divided into four layers (B0, B1, B2, B3), the bandwidth of the node on each layer is a multiple of four RBs, and each parent node is a multiple of its child node, and the multiple is the number of child nodes contained by the parent node. As shown in FIG. 1, one parent node of layer B0 corresponds to two child nodes of layer B1, each child node of layer B1 also corresponds to two child nodes of layer B2 as a parent node, and each child node of layer B2 further corresponds to three child nodes of layer B3 as a parent node (how many child nodes a parent node includes is determined by the SRS bandwidth configuration of the cell), and the bandwidth values of all nodes in the same layer are the same, the root node, i.e. the first layer (layer B0 in the figure) is the SRS bandwidth of the whole system, and the node bandwidth granularity of the last layer is four RBs.
The SRS sequence is mapped to the subcarrier of the corresponding bandwidth by adopting a Comb structure (i.e. the SRS sequences are either all mapped to odd-number subcarriers, or all mapped to even-number subcarriers, thus forming a Comb structure). As the subcarrier of RB0 shown in FIG. 1, the black positions represent even-number subcarriers, while the white positions represent odd-number subcarriers. One SRS tree can be divided into an odd tree (composed of all subcarriers at white positions in the SRS tree in FIG. 1) and an even tree (composed of all subcarriers at black positions in the SRS tree in FIG. 1) by this Comb structure. The starting position of the SRS sequence of the UE on the odd tree in the frequency domain is an odd-number subcarrier, and the whole sequence is only distributed on odd-number subcarriers; the starting position of the SRS sequence of the UE on the even tree in the frequency domain is an even-number subcarrier, and the whole sequence is only distributed on even-number subcarriers. Therefore, the length of the SRS sequence of the UE is half of the number of all subcarriers within the allocated SRS bandwidth. The continuous length of bandwidth in each layer (B0, B1, B2, B3) in FIG. 1 can be considered as one node, for example, the SRS odd tree corresponding to layer B0 has only one node (meanwhile the even tree also has one node), and the SRS odd tree corresponding to layer B1 has only two nodes, and so forth.
It is regulated in the LTE protocol that the SRS transmission period of the UE has eight types, which are {2,5,10,20,40,80,160,32} specifically, with the unit of ms. The cell specialized subframe offset under the corresponding cell specialized subframe configuration period is the subframe that can be used by the UE of the cell for transmitting SRS. Since the SRS bandwidth resources are limited and the SRS bandwidth of the whole system cannot be allocated to each UE, in order that the base station obtains the channel information of the frequency band that is not allocated to the UE, it is allowed in the LTE protocol that the UE obtains the channel information of other frequency bands by means of frequency hopping. Of course, the UE can also adopt non-frequency hopping manners. Each UE is configured with one frequency hopping bandwidth, and whether the UE performs frequency hopping on the SRS bandwidth of the whole cell or on part of the bandwidth or UE doesn't perform frequency hopping is determined according to the configured frequency hopping bandwidth and the size of bandwidth for the UE transmitting the SRS.
According to the above various usable technical conditions, the SRS resource allocation may be implemented in many different manners, and meanwhile due to the influence of tree structure, frequency hopping and different SRS transmission periods and so on, SRS resource allocation also has many limitations. For example, as for the odd tree of the SRS tree, the premise that its parent tree can be allocated to the UE is that none of its all child nodes has been allocated yet, that is, as long as any one of the child nodes of the parent node has been allocated, this parent node cannot be allocated as a whole, but its child nodes, as a whole, are allocated to a UE with the same bandwidth as that of the child nodes; as for the odd tree of the SRS tree, if UEs with various SRS transmission periods are included, the frequency hopping of each UE will not be synchronous due to different periods, which will lead to overlapping of bandwidths for different UEs transmitting SRS, thus causing interference. If UEs with different periods are transmitted on different subframe offsets, since there are various UE SRS period configurations, and the available subframe offsets are not sufficient, and more importantly there are too many configuration types of subframe offsets, the resource multiplexing process of SRS will be very complicated; likewise, there also exists the same problem for the even tree of the SRS tree.